Make Array.indices extension property, move to stdlib

This is not something that needs to be intrinsified. Note that compiler
optimizations are still possible and the fact whether 'indices' is a member or
an extension is irrelevant to the optimizer

compiler/testData/codegen/box/arrays/indices.kt

@@ -1,9 +0,0 @@
-fun box(): String {
-    val a = Array<Int>(5, {it})
-    val x = a.indices.iterator()
-    while (x.hasNext()) {
-        val i = x.next()
-        if (a[i] != i) return "Fail $i ${a[i]}"
-    }
-    return "OK"
-}

compiler/testData/codegen/box/arrays/indicesChar.kt

@@ -1,9 +0,0 @@
-fun box(): String {
-    val a = CharArray(5)
-    val x = a.indices.iterator()
-    while (x.hasNext()) {
-        val i = x.next()
-        if (a[i] != 0.toChar()) return "Fail $i ${a[i]}"
-    }
-    return "OK"
-}

compiler/testData/codegen/box/arrays/kt2997.kt

@@ -5,55 +5,47 @@ fun foo(a: Any): Int {
         a.get(0)
         a.set(0, 1)
         a.iterator()
-        a.indices
         return a.size()
     }
     if (a is ShortArray) {
         a.get(0)
         a.set(0, 1)
         a.iterator()
-        a.indices
         return a.size()
     }
     if (a is ByteArray) {
         a.get(0)
         a.set(0, 1)
         a.iterator()
-        a.indices
         return a.size()
     }
     if (a is FloatArray) {
         a.get(0)
         a.set(0, 1.toFloat())
         a.iterator()
-        a.indices
         return a.size()
     }
     if (a is DoubleArray) {
         a.get(0)
         a.set(0, 1.0)
         a.iterator()
-        a.indices
         return a.size()
     }
     if (a is BooleanArray) {
         a.get(0)
         a.set(0, false)
         a.iterator()
-        a.indices
         return a.size()
     }
     if (a is CharArray) {
         a.get(0)
         a.set(0, 'a')
         a.iterator()
-        a.indices
         return a.size()
     }
     if (a is Array<*>) {
         if (a.size() > 0) a.get(0)
         a.iterator()
-        a.indices
         return a.size()
     }